package network;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class UDPEchoServer {

    // 创建一个socket对象
    private DatagramSocket socket=null;
    public UDPEchoServer(int port) throws SocketException {
        socket=new DatagramSocket(port);
    }

    //通过start来启动服务器的核心流程
    public void start() throws IOException {
        System.out.println("服务器启动!");
        while(true) {   //通过一个死循环不停地处理客户端的请求
            // 1. 读取客户端的请求并解析
            DatagramPacket requestPacket=new DatagramPacket(new byte[4096],4096);
            socket.receive(requestPacket);

            // 上述收到的数据是二进制byte[]的形式体现的,后续代码如果要进行打印之类的处理操作,需要转成字符串数组才好操作
            String request=new String(requestPacket.getData(),0,requestPacket.getLength());

            // 2. 根据请求,计算响应,由于此处是回显服务器,响应就是请求
            String response=process(request);

            // 3. 把响应写回到客户端
            DatagramPacket responsePacket=new DatagramPacket(response.getBytes(),response.getBytes().length,
                    requestPacket.getSocketAddress());
            socket.send(responsePacket);

            // 4. 打印日志
            System.out.printf("[%s,%d] req=%s,resp=%s\n",requestPacket.getAddress(),requestPacket.getPort(),
                    request,response);

        }
    }
    //实际中,这个处理过程会非常复杂
    public String process(String request){
        return request;
    }

    public static void main(String[] args) throws IOException {
        UDPEchoServer server=new UDPEchoServer(9090);
        server.start();
    }
}
